This invention relates to containers and methods for forming reusable and/or disposable plastic containers.
In my earlier filed co pending application there is disclosed a container construction comprised of upper and lower portions, the lower portion including self-supporting side walls and a bottom wall, and the upper portion including a flexible and non-self-supporting portion, whereby the container is able to stand in an upright orientation, while the upper portion may be gathered and closed in the manner of a thin film bag. To this end, the side walls of the lower portion are preferably formed of a plastic material of predetermined thickness, greater than the thickness of the upper portion. The wall thickness of the lower portion can also be modified as desired so as to be sufficient to avoid puncturing by materials disposed within the container, and to afford sufficient strength and rigidity to maintain the container in its intended configuration without significant distortion or flexing.
The upper portion of the container preferably constitutes a flexible, integral extension of the side walls of the lower portion. That is, the side walls and the upper portion are of unitary one-piece plastic construction, one with the other, with the upper portion constituting a thin film of plastic material forming a continuation of the side walls. The flexible upper portion terminates in a free end which, in accordance with this continuation-in-part application, may be provided with an integral press-lock closure by which the open end of the container may be closed, opened and reclosed as desired.
The container of this invention is preferably formed by blow-molding. Blow molding is a well known technique for forming hollow objects wherein air, and sometimes nitrogen, is used to expand an extruded parison within a female mold cavity. Within the blow molding art generally, three specific processes are employed: injection blow molding, stretch blow molding, and extrusion blow molding.
In a typical injection blow molding process for forming, for example, a small bottle, a plastic resin in molten form is injected into a preform mold to form a parison. Typically, the preform mold is shaped to provide an accurate, finished neck area and a partially shaped body portion The preform is then transferred to a blow mold where the preformed neck area is confined and the body portion expanded or blown to its final desired shape. While this process is particularly useful for small plastic bottles wherein at least a portion of the bottle neck has an intricate or complex design detail, usually in the neck area, it is nevertheless a costly process, primarily because of the detailed tooling configurations required.
In stretch blow molding, an extruded parison is stretched longitudinally prior to blow molding within a closed mold cavity.
Extrusion blow molding, on the other hand, is a less costly process typically used for forming large containers, tanks, etc. In the extrusion blow molding process, melted plastic resin is extruded, usually as a tubular parison, into free air and thereafter clamped between a pair of mold halves which together define a mold cavity. A blow pin is then inserted into the interior of the mold (typically through what will become the open container end) for supplying air which expands the parison against the interior surfaces of the mold cavity.
It is also known in the prior art to attach, such as by heat sealing, separately extruded closure strips along the open end of a thin film bag or container. Here again, however, multiple manufacturing and assembly steps are required.
It has now been discovered that an extrusion blow molding process may be employed to form a container as disclosed in my prior co-pending application which also includes an integral press-lock closure which is considerably less costly and simpler to manufacture than the multiple step processes of the prior art.
Specifically, in the process aspect of this invention, the plastic material is extruded from a die head to form a tubular parison. When extruding the material, the die head preferably extrudes a relatively thick first parison section which eventually will form the lower, self-supporting portion of the container. The die head is then adjusted, automatically, to extrude a thinner second parison section which eventually will form the upper flexible portion of the container. The die head is then adjusted again to extrude a thicker third parison section, having a wall thickness substantially identical to the first parison section, and which will ultimately form the integral press-lock closure portion of the container. After extrusion, opposed mold platens are moved into position on either side of the parison, and are then closed to clamp the parison within the mold. After the parison has been severed just above the mold, a blow pin or other suitable air supply device is inserted into the mold and parison. Insertion of the blow pin or other device may take place below the extrusion die head, or at a separate workstation to which the mold platens may be transported. Either arrangement is suitable and both are known in the extrusion blow molding art.
The parison is then inflated by introducing air through the blow pin or other device to expand the plastic material against the interior wall surfaces of the mold. In accordance with this invention, the mold halves are formed with complementary male and female surface portions, respectively, which serve to form, during blow molding, a press-lock closure in the first parison section which ultimately forms the open end of the container.
Specifically, the mold cavity is provided with a projecting rib extending about one-half of the cavity, and a rib receiving recess about the other half of the cavity. It will be understood that the projecting rib and complementary recess are formed along a continuous line adjacent what will eventually become the open end of the blow molded container.
The projecting rib formed on the one mold half will result in a substantially hollow, rib-like projection facing radially inwardly about one-half of the container, while the recess or groove formed in the other mold half will form a complementary recess facing radially inwardly about the other half of the container.
Upon subsequent removal from the mold, there is thus formed a unitary one piece container having a flexible, non-self-supporting upper portion provided with an integral press-lock closure, and a lower portion having self-supporting side walls and a bottom wall.
The rib and groove configuration are sized such that, when the open end of the finished container is flattened, the rib may be pressed into a friction fit or snap-fit type engagement with the opposed recess to close the container.
It will be understood, of course, that this invention, insofar as it relates to extrusion blow molding of an integral press-lock closure, is not limited to the container constructions disclosed in my co-pending application. In fact, the invention is applicable to the manufacture of virtually any single or multi-layer plastic container or enclosure which may be blow molded, and which is sufficiently flexible to permit the open end thereof to be drawn inwardly or flattened, to form, in effect, two sides which can be releasably locked by an arrangement as disclosed herein.
For example, the invention encompasses the manufacture of non-self-supporting plastic film bags by blow molding where the thickness of the bag adjacent the open end is increased to accommodate an integral press-lock closure. In addition, the invention encompasses the manufacture of self-supporting containers by blow molding, which containers are nevertheless sufficiently flexible to take advantage of the integral press lock closure of the invention. Such containers may be of uniform thickness, including the press lock area, or the latter may have a different thickness.
Thus, the invention provides a relatively simple and less costly process for forming flexible containers with integrally formed closures, which enable a container to be closed, opened and reclosed as desired. Other objects and advantages of the invention will become apparent from the detailed disclosure of the invention which follows.